We experimentally explore emergent phenomena regulated by the higher organization principle of topological order, using the tools of condensed matter physics. Our main research interest is to understand topological quantum matter with and without interactions from the macro to the nanoscale, where quantum effects give rise to unusual electronic and thermal transport properties.
Of particular interest are topological materials in which the electronic excitations are effectively described by relativistic quantum field theory. Within the topological band structure, electrons can form states that collectively behave as relativistic Dirac, Weyl or Majorana fermions, enabling to experimentally probe exotic quantum effects that have previously only been discussed in the context of high energy physics.
We seek to gain experimental insights to quantum anomalies, such as the chiral and gravitational anomaly, emergent gravity, novel particle excitations, spontaneous symmetry breaking and bounding transport. Topological states are often associated with a relevant physical length scale (e.g. mean free path, coherence or Fermi wave length). We investigate how the electronic system changes as its physical dimension is tuned below that length scale.
While relativistic quantum field theory is traditionally investigated in particle physics and cosmology, which are rather observational sciences, we employ state-of-the-art growth, device fabrication and measurement techniques of solid state research and industry to design effective environments for topological quasi-particles.
Our research is at the interface between physics, materials science and device engineering, and thus our efforts are naturally collaborative. We form strong international collaborations with theoretical physicists, material synthesis experts and device engineers around the world.
Technically, our group operates as follows:
First comes the idea. Then the required material is selected with regard to the scientific question. We use chemical vapor deposition to grow bulk single crystals, vapor-liquid-solid growth for nanowires and plates as well as exfoliation techniques. Subsequently, the structure and chemical composition of the grown material is characterized. Here, we gain a lot from the material science expertise and the infrastructure at our host institute. If its high quality is confirmed, the material will be implemented into a device, comprising field-effect structures, spin-valves and Weyl-Weyl semimetal and Weyl-superconductor heterostructures. For this purpose, we make use of the new clean room at the MPI CPfS, including laser and electron beam lithography, sputter and wet etch techniques, and contact metal deposition facilities. Finally, electrical, thermoelectrical and thermal transport experiments are performed on the devices at high magnetic fields and cryogenic temperatures.